Electromagnetic clutch and brake servo mechanism



- April 1952 R. J. HERST ET AL 2,594,775

ELECTROMAGNETIC CLUTCH AND BRAKE SERVO MECHANISM Filed Aug. 30. 1949 5 Sheets-Sheet l JWMM April 29, 1952 R. J. HERST ET AL 2,594,775

ELECTROMAGNETIC CLUTCH AND BRAKE SERVO MECHANISM Filed Aug. 30, 1949 5 Sheets-Sheet 3 Patented Apr. 29, 1952 UNITED? STATES PATENT OFFICE;

ELECTROMAGNETIC CLUTCH AND BRAKE SERVO MECHANISM.

Richard J. Horst, Chicago, and Stanton Hi Petty,

Evanston, Ill., assignors to Robert OLBuehler, doingbusiness as Buehler and Company;

Application August 30, 1949,'SerialNo.-113,181

\ 10 Claims.

1 Thisinvention relates to servomechanisms of the clutch-brake type,-and the principal objects of. the ,inventionare' to. provide a mechanism of this type .Whichis sturdy, accurate, and reliable; .which has little tendency to .hunt? its stabilized position; which has relatively small rotational inertia so that starting is quickfand overshoot ing ofbalanced position is minimized; which iis.

made up of twin units with a resultant saving in the cost of parts; and which is so constructed and arranged that extremely close tolerances maybe established and maintained for :the relatively moving parts, and particularlyrforthe .air gaps which. are associated with :the electromagnetic driving clutches.

Further and other objects WiIlLbecQme apparentas the disclosure proceeds and the-description isread in conjunction with theaccompanying Figure .5 is anvend elevational view showing the manner in which a number of servomechanisms maybe stacked for multiple operation;

Figure 6 is a perspective view showing the iron plate which forms a closurefo'r the coil hous Figure '7 is a perspective view-showing the coil housing; and

Figure 8 is a view showing. the split core for the electromagnetic clutches...

The showing, .in.the drawingsof'a preferred embodiment of the inventionend the; specific description thereof which follows are in compliance with Section488-8 of the .RGVlSEGYStBLtHtBSEIIG should not be construed :asimposing limitations on the appended claims except as maygbe requiredbythe prior art.

A servomechanism, although having manyiapplications, most'frequentlyserves as a position selector for a rotary shaft; that is, the output shaft of the servomechanism is intended to fol-.

low precisely the movement'and position of a remote input shaft. This is accomplished in most cases by a bridge circuit whichmdetects movementof one: shaft relative -,-to the-othenenda reversihleelectric motor-which :respondsgto un-i 2 balanced conditionsin the bridge circuit to move the output or control shaft oftheservomecha-anism in conformity with movements of the input shaft.

A a servomechanism employing an induction-- motor as the =means for controlling position-of: the output shaft has the inherent disadvanta e that the output shaft, inmoving to the desired position, is likely to overshoot its mark, causing' the shaft to "be turned in the opposite direction.- and againproducing forces which tend to cause the shaft to :overshoot its mark The result is that the. mechanism is. continually hunting its stabilized 'positionand this constant movement of: the output'shaftnot: only destroys the accuracy; of the servomechanism, but also; produces need-' less wear.

By contrast, a servomechanism of the clutch-:. brake type, such-as shown in the copendingape: plication of Francis E. Edwards,- JlL, SerialNo': 34,700, filed June 23, 1948, has little tendency 'to oscillate about its balanced 'position and rarely. overshoots its mark because of the action of the. brake Which is automatically applied when thedriving clutches are disengaged. Sometimeswh'en the output shaft is required to make an extensive adjustment due to corresponding move ment of the input shaft, the inertia of the shaft with the load that it, carries will produce slight overshooting of the mark, but this is rapidly corrected by theaction of the reverse clutch, and. the shaft soon finds its adjusted position and; remains in that position, by the. action of the brake, x as long as the system is undisturbed.

The presentinvention represents an improve-. ment in the. clutch-brake type of servomechanism disclosedin the Edwards application aboveidentified, and is particularly suited for volumeproduction.- A mechanism of this type requires extremely close tolerances for satisfactory op-- eration, and the present invention provides "an arrangement-whereby these tolerances may be readily obtained and maintained.

Referring 'now' to Fig. 4, it will be seenthat the servomechanism, generally designated l0, comprises an output shaft l I, preferably of stain-a less steel or cold rolled steel, to which spaced. discs l2 and !3' are secured by pins M. The discs are preferably made of non-magnetic stainless steel, and the forward face I5 of each disc (conev sidering the right hand side. of the .unit as the front end) is ground to complete .flatnessr:

The shaft is supported at its endsiby bearings-i.

l5 and ll, these--bearings preferablybeing. made of Oilite and being self-lubricating, although oil holes may be provided, if desired.

The servomechanism casing comprises a number of sections includinga rear housing l8 having a removable end plate IS, a clutch housing 20, an iron plate 21, a cup-shaped coil housing 22 constituting a part of the iron circuit for one of the electromagnetic clutches, a second clutch housing 23, another iron plate 24, and a second cup-shaped housing 25 which closes the front end of the unit.

These parts will be described in more detail in conjunction with the functions which they serve.

The servomechanism comprises essentially two electromagnetic clutches, generally designated 26 and 2'1, which are adapted to apply a driving force to the shaft I i in a selected direction. The clutch 26 comprises a gear 28, preferably of laminated linen-base phenolic, and which for convenience will be referred to as the counter-clockwise clutch gear. The gear has pressed into it an Oilite bearing 29 which mounts the gear loosely upon the shaft H for rotary movement relative thereto, and the gear is constantly driven by a pinion gear 30 (Fig. 2) mounted on a countershaft 3! connected directly, through a universal coupling 32, to a motor (not shown).

A clutch ring 33 is secured to the rear face of the counter-clockwise clutch gear 28, and the mounting of the gear on the shaft is such that the gear may be moved slightly to the left to bring the clutch ring into driving engagement with the planar face I5 of the clutch disc I 2.

The output shaft H is also capable of slight longitudinal movement-its movement to the left or rear being limited by an adjustable stop 34 threaded into the cover plate [9, and movement to the right being limited by a brake ring 35 which is mounted on the rear face of an inwardly extending flange 36 of the clutch housing 20.

The clutch ring 33 and the brake ring 35 are both made of high-grade cork, and are firmly secured to the part with which they are associated, i. e., the clutch ring 33 is cemented to the gear 28, and the brake ring 35 is cemented to the clutch housing 20. Obviously the brake ring 35 and/or the clutch ring- 33 could be secured to the disc i2, if desired, and this variation should be considered as an equivalent structure.

The shaft I I is normally biased to the right or braking position by a leaf spring 31 which is anchored at 38 and bears against a ball bearing 39 fitted into the end of the shaft H. The extent of the bias is determined by the pressure applied to the spring 31. by adjusting screw 40, and this adjustment is critical with respect to the action of the electromagnetic clutches 25 and 27. Lock nuts 4% maintain the adjusting screws 34 and 40 in their desired adjusted position.

Movement of the counter-clockwise clutch gear 28 with its clutch ring 33 into driving engagement with the disc i 2 is accomplished by an electromagnet comprising a coil 42 telescoped over the shaft H and seated within the cup-shaped housing 22. The iron circuit for the electromagnet includes not only the iron plate 2i and housing 22, but also a movable iron core 43 which has pressed-in phenolic bearings 44 at its outer ends which are telescoped over the shaft II and are rotatable and longitudinally slidable with respect thereto. All parts of the iron circuit are slotted to reduce eddy currents, and speed up action of the electromagnetic clutch. This is shown best in Figs. 6, 7 and 3.

The core 43 is held in the desired spaced relation from the gear 28 by a loose-fitting brass spacer 45, and the critical air gap which closes or is reduced in size when the coil 42 is energized is shownat 43. A loose-fitting brass spacer 41 is mounted at the front end of the core 43 to keep the core properly spaced from the adjoining disc l3, although this distance is not critical.

It should be understood that the air gap 46 is critical in the sense that when the associated coil 42 is energized to set up a magnetic force tending to bias the core 43 against the spacer 45 which in turn is then biased against the hub 29 of the gear 28, the air gap 46 is then defined and at this instant must be sufiicient in extent to permit further movement of the core 43 to the left to not only bring the gear 28 into engagement with the disc l2, but also displace it with respect to the brake ring 35. In other words, at the instant that the coil 42 is energized, a magnetic force is set up which moves the core 43 to the left and clamps the core 43 and spacer 45 against the gear 28, thus providing the critical air gap required for the actual engagement of the clutch and displacement of the disc 12 away from the brake ring 35. Obviously, when the clutch is disengaged, there is no need for a critical air gap or to maintain the parts in this relationship, except that permissive movement of the core 43 to the right is restricted suificiently by spacer 41, so that subsequent energization of the coil 42 will always pick up the core 43 and bias the associated parts to the left.

It will be seen that when the coil 42 is energized, the magnetic flux travels through the iron circuit as shown by the arrows, and the core 43 is moved to the left tending to close the air gap 43. This movement of the core is transmitted through the spacer 45 to the clutch gear 28 and clutch ring 33, the latter lifting the disc 12 from the brake ring 35 and transmitting the counterclockwise driving force of the gear 28 to the shaft I i. This movement is on the order of a few thousandths of an inch, possibly .003 of an inch, and from this may be seen the precision character of the device. Upon tie-energizing the coil 42, the spring bias on the shaft immediately forces the disc l2 against the brake ring 35, causing the shaft to stop rotation immediately.

In a similar manner, the electromagnetic clutch 21 is adapted to transmit a driving force to the output shaft I l, but in this case, the driving force is in a clockwise direction. The clockwise gear is shown at 48, and it is driven in this direction by a pinion gear 49 which is mounted on the countershaft 3| and drives through a reversing gear 50 which is in mesh with the gear 48.

The gear 48 has a pressed-in Oilite bearing 5| which loosely mounts the gear on the shaft II for rotation thereabout, and the rear face of the clutch gear has a clutch ring 52 which is adapted to make contact with the clutch face 15 of the disc I3. Since the clutch discs l3 and 12 are firmly secured to the shaft II, it is unnecessary to provide a brake disc on the clutch housing 23, although one could be provided for cooperation with the disc l3 if desired.

The clutch gear 48 with its clutch ring 52 is moved into driving engagement with the clutch disc 13 by an electromagnet which includes a coil 54 and an iron circuit similar in all respects to the one associated with the clutch 26. The movable core 55 associated with the coil '54 has pressed-in phenolic bearings 56 and the operating air gap is indicated at 57. The movable core 55 is held in proper spaced-relation to the gear 48 by a brass collar or spacer 58, and a similar to zthezleftinxtits attemptzwto; close thep airigapss 51:; $131118 movement; .beinggtransmitted. through spacer .58 to. the. gear .4 8 and clutch ring-52., iwhic moves;- -zthe.-'-shaft"' :assemblyl slightly. g-togithfi; .rlei tothereby lift: theclutchdiscd 2 from the; brake ring. 3 Srthereby permitting clockwise clutchfge, 4M0. transmit correspondingrotationito the: shaft I is,Theiironzcircuitfor the clutch-:21. is-slotted currentmand minimizei time -:lag; ;in athewioperae tionzof..-the--clutch,. and .the.zwidth =of air: in?! corresponds. to. that-oi air gap..14fiyipreviouslygriea, scribed:

bolts-.60. as.- shown 'on--- the drawings; '1

Since --the shaftl I" travels but; .two orwthree-s thousandthsof an inch inmovingfromits braked i position-to-ritse driving- .position, :itis of; utmost;.-,

importance that all components which- .-.fix.-.;thc:v25

spacing. of .the :parts along .the shaft. be made with precision and A properly ;-assemb1ed. The present construction permits such-.1 precision .300; be built. into the --servomechanism in .-.a :-.-manner.;; consistent; withmass production rtechniques. i

Invassembfing the servomechanism; the;s-tie.-=: boltsqfioeare first: fitted with-nutsat- :the ream-.7. endwand the rear housing .-I 8. is .thenrmounted -on thetie bolts Theshaft-l lwith the cl-utch discr. pinned in place but with .clutch .disc.l3 -re; moved. is then .slippedinto ithe...bear-ing-.;| 6 zflndfb.

temporarily 1 supported @atiitsiiront 1 end; Thar-f5 clutch housing ;2 0-, which, .like .the end housing-;

I B,... is .,.p1 eferab1y ,made -.of-. aluminum;- slipped inv .place on the: :tie sboltsp the; operatingface. of the. bralcecdiscafihaving p viously been ground to-propcr. distance. from.-.the.-.-. front face [of the clutch housing? 20-. Theqgearr-i; 28...isi then slipped in place,.and iniorder. for the; z:

is .t-gthensr r in shownr;in-:.;: i .e ,rio :.multipleronerationnwith thc;.c1utch:c=eea1tsrot-adj acenti unit mxtendin sli h ly-tb yond-itherexternal rfacei of. he casin and -:'intermeshing: for. carry D QI W' Qm drives-s 5 from one unit to another, andnwith only onei of tangentiahto the.--externa1-1 facesof ,the casing;

We claim I 1 s In; a iservomechanismraof. "the clutch-brake v type,- -a shaft'having.spacechdiscsmountedthere-c on; a icasing ovencthe ,shaft proyidingbearings; for. its .vsuppont; a -brakez-ring ..pn ;-.the. casingon1 I inEIhe-sameQmannerasclutch-:26; toreducemddy 152a eable1withMoney-of said-discs when. the shaft is moved-ilongitudinally along its axis .in .one;' 1 direction; .spring means .biasingz the shaft in said.- direction, forward -:-an.d v.reverse- ..clutch ,mecha-L v hismsfor. rotating; the. shaft. in a selecteddirec-r The-entire wassembla'ge is :held: to qtherzby tiercmmtionvone .such-.mechanismSeeing. associated with eachgdisc, said -.clutch .lm echanisms each corn i pifising a gear. .,rotatably mounted on .thesshaft :bias,-. and.:. an .electromagnet. for. effecting said "clutch. rengaging movementwsaid .relectromagn t,

comprising.- ,a ...coil. ,telescoped over the ,,shaft, a movable core within the coil and... also flUGIBSQODQ dw amroverntheshaft, and an iron-cimliiticlosed c p f r.an--opcratin sairean 2..eIn,.va seryomechanism ,of.-..'the clutch-brake.-

type, a shaft having spaced-discs .mounted there -i ons a .casing .overuthe.shaftprovidin bearings for saints. 511990 11 a brake lingo. cm the. casing. engageab1e ...wi th. one. of .-said-..discs....vvhen.theishaitpis. movedlongitudinally; along.- itsaxis. in .onesdiremn. tion,.spring.7 means. biasing. .the. shaft: in said direc i m i rwardiand reverse clu ch.mechanisms... 40x50! rotating. theshaftin; a selmteddirection one such .lmechanism being associated. with, each. .disc,

said. clutch mechanisms. each. comprising. a gear:

rotatably. moun d on t e. shaft .a friction clu ch...

' ring .on the gearengageablewiththe juxtaposed.

face .of.the.-c1utch ring- 33 to be. properly spacem isndiscpwhen thegefq is moved .inza direction 0PpQ-..

with lrespect to ethefrontface. of the Oilite beans.

ing 29,'the clutch ring is ground to provide-thei desired dimension between. .these -.tw.o wfaeesor Thea-soft iron .platel l. isethen =put intoqplacey critical with, respect to the 'oper-atingr. .aire gap- 46, :itis surface. ground .to close tolerance The;

slippedirito'. .place...0ver. the shaft ll .andebotha site to that of the shaft bias, and anelectromagnetior effectingsaid clutchengaging movement; 1 said electromagnet comprising a coil telescopedv over-the-shaft; amovable-core Within-the coil and since theiithicknessh of. ,thisgplatehis.very m. .and also telescoped over-the shaft;and an iron-- circuit closed-except for-an operating -air gap" and including th'ecore and at least a portion-of brassspacer .4 5 and. the magnet corci43, are then- 1.

said.- casing.

endsLoithe. spacer. are. preferably groundsmthat: rod typewa shaft having spaceddiscsmounted therethe. Ieanend oi. the. magnetv core. A 3sissproperlya.

spaced fromthe; plate -2 I. .toiprovide. the .vdesiredz s air'gap. .46.

After-slipping. .the washers-.41 ,in.'.pla'c.e, lather,

bmacasing over theshaftjprovidingbearings for itsisirpportra :brake ring on thecasing engageable' withgone -10f: said .discs. whenvtheshaft is moved longitudinally; "along cits: .1 axis in one. direction cup-.shaped iron circuit] 2 isthenmounted-on ,the. ioo springqmeans biasing; thershafiti in said direction.-

tie' bolts and. then. the. disc, i3 .is' slipped- ..on the..... shaft and secured thereto by. thep'm. l.4.... Matched; setsiof: discsjandishaftsare useds'o thatrwhenihew discv i3 is. pinned to .theshait; it1is...sp.aced.from;.. the. rear disc. .I 2. the. desired distances 65,..tatahl .mountedgon-the shafn a fri.ct.ion-iclut,ch

. ring .-on-the. gear;ienga eabletwi hit e;jux aposed .sc:: whenrthezz an-is moved i zaidirection1on remainin assembly -,oncr ations .aremore or. less obviouspwithithe. aluminum clutchlhouseo in'g. 23' being then. slipped into ;p1ace, thereafter; the clockwise clutch gear ,48',1iron .platcimspacern 58;?magnet core 55','.'washer.-59;iand.then..finallyf .7o said.electromagnet.comprising. a coil telescoped' over; the. .shaftwaimovableicore ,within the. coil... and ,also .telescoped .over .the.-.,sh.ait, .and-i aniron l u the iron coil.housingg25,"afterjwhich"nuts..-ar.e..

applied .to the front endslof the. tie'ioolt's. and),

the entire assembly firmly clampedto ether....

Ones-advantage not .thespresent;cqnstructioniis' forward- .and reverseclutch :mechanisms for TO.-

' tating ;the.- shaftin aaselected direction,- one such 'mechanism-zbeingr associated with leachidiscwsaid clutch mechanisms:- .-.each-.- comprising .a gear r -i;

; positei-to-rthatzof, the I shaft bias,.;an electromagnet; f or,. efiectingr. said clutch engaging... movement,

a cesses imics.

said member except for an axial opening, and a spacer within said opening and between the core and the gear for fixing the position of the core with respect to said plate to thereby establish the operating air gap.

4. In a servomechanism of the clutch-brake type, a shaft having spaced discs mounted thereon, a casing over the shaft providing bearings for its support, a brake ring on the casing engageable with one of said discs when the shaft is moved longitudinally along its axis in one direction,

spring means biasing the shaft in said direction,-

forward and reverse clutch mechanisms for rotating the shaft in a selected direction, one such mechanism being associated with each disc, said clutch mechanisms each comprising a gear rotatably mounted on the shaft, a friction clutch ring on the gear engageable with the juxtaposed disc when the gear is moved in a direction opposite to that of the shaft bias, and an electromagnet for effecting, said clutch-engaging movement, said electromagnet comprising a coil telescoped over the shaft, a movable core within the coil and also telescoped over the shaft, and an iron circuit closed except for an operating air gap, said casing being made in a plurality of interfitting face ground sections whereby the exact positioning of elements of said mechanism along the shaft is facilitated.

5. In a servomechanism of the clutch-brake type, a shaft having spaced discs mounted thereon, a casing over the shaft providing bearings for its support, a brake ring on the casing engageable with one of said discs when the shaft is moved longitudinally along its axis in one direction, spring means biasing the shaft in said direction, forward and reverse clutch mechanisms for rotating the shaft in a selected direction, one such mechanism being associated with each disc, said clutch mechanisms each comprising a gear rotatably mounted on the shaft, a friction clutch ring on the gear engageable with the juxtaposed disc when the gear is moved in a direction opposite to that of the shaft bias, an electromagnet for effecting said clutch-engaging movement, said electromagnet comprising a coil telescoped over the shaft, a movable core within the coil and also telescoped over the shaft, and an iron circuit closed except for an operating air gap, the spring means for biasing the shaftcomprising a leaf spring extending across the end of the shaft, and means for adjusting the tension of said spring.

6. In a servomechanism of the clutch-brake type, a shaft having spaced discs mounted thereon, a casing over the shaft providing bearings for its support, a brake ring on the casing engageable with one of said discs when the shaft is moved longitudinally along its, axis in one direction, spring means biasing the shaft in said direction, forward and reverse clutch mechanisms for rotating the shaft in a selected direction, one such mechanism being associated with each disc, said clutch mechanisms each comprising a gear vrotatably mounted on the shaftga friction clutch ring on the gear engageable with the juxtaposed disc-when the gear is moved in a direction opposite to that of the shaft bias, an electromagnet for effecting said clutch-engaging movement, said electromagnet comprising a coil 'telescoped over the shaft, a movable core within the coil and also telescoped over the shaft, and an iron scircuit closedexcept for an opera-ting air'gap. and means for limiting movement of the shaft in an axial direction opposite to that of the spring bias.

7. In a servomechanism of the clutch-brake direction, spring means biasing the shaft in'said' direction, forward and reverse clutch mechanisms" for rotating the shaftin a selected direction, one such mechanism being associated with each disc, said clutch mechanisms each comprising a gear rotatably mounted on the shaft, a friction clutch ring on the gear engageable with the juxtaposed disc when the gear is moved in a-direction opposite to that of the shaft bias, an electromagnet for effecting said clutch-engaging movement, said electromagnet comprising a coil telescoped over the shaft, a movable core within the coil and also telescoped over the shaft, and an iron circuit closed except for an operating air gap, and adjustable means for limiting movement of the shaft in an axial direction opposite to that of the spring bias.

8. In a servomechanism of the clutch-brake type, a shaft having spaced discs mounted thereon, a casing over the shaft providing bearings for its support, a brake ring on the casing engageable with one of said discs when the shaft is moved longitudinally along its axis in one direction, spring means biasing the shaft in said drection, forward and reverse clutch mechanisms for rotating the shaft in a selected direction, one such mechanism being associated with each disc, said clutch mechanisms each comprising a gear rotatably mounted on the shaft, a friction clutch ring on the gear engageable with the juxtaposed disc when the gear is moved in a direction oppoe site to that of the shaft bias, and an electromagnet for effecting said clutch engaging movement, said electromagnet comprising a coil telescoped over the-shaft, a movable core within the coil and also telescoped over the shaft, and an iron circuit closed except for an operating air gap, said discs on the shaft forming no part of said iron circuit.

9. In a servomechanism of the clutch-brake type, a shaft having spaced discs mounted thereon, a substantially rectangular casing over the shaft providing bearings for its support, a brake ring on the casing engageable with one of said discs when the shaft is moved longitudinally along its axis in one direction, spring means biasing the shaft in said direction, forward and reverse clutch mechanisms for rotating the shaft in a selected direction, one such mechanism being associated with each disc, said clutch mechanisms each comprising a gear rotatably mounted on the shaft, a friction clutch ring on the gear engageable with the juxtaposed disc when the gear is moved in a direction opposite to that of the shaft bias, an electromagnet for effecting said clutch-engaging movement, said electromagnet comprising a coil telescoped over the shaft, a movable core Within the coil and also telescoped over the shaft, and an iron circuit closed except for an operating air gap, said gears having their pitch line substantially tangential to the external face of the casing, whereby a number of units may be stacked together with gears intermeshed for transfer of power from one unit to the adjacent unit.

type, 'ashaft havingspace'd discs "mountedwhere on, a casing over the shaft providing bearings for its support, a brake ring on the casing engageable with one of said discs when the shaft is moved longitudinally along its axis in one direction, spring means biasing the shaft in said direction, forward and reverse clutch mechansms for rotating the shaft in a selected direction, one such mechanism being associated with each disc, said clutch mechanisms each comprising a gear rotatably mounted on the shaft, a friction clutch ring on the gear engageable with the juxtaposed disc when the gear is moved in a direction opposite to that of the shaft bias, and an electromagnet for effecting said clutch engaging movement, said electromagnet comprising a coil telescoped over the shaft, amovable core within the coil 10 and also telescoped over the shaft, and an iron circuit closed except for an operating air gap. at least a portion of said iron circuit being slotted to minimize eddy currents.

RICHARD J. HERST. STANTON H. PETRY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 744,423 Steckel Nov. 17, 1903 2,464,129 Goettisheim Mar. 8, 1949 2,490,044 Gabarini et al. Dec. 6, 1949 

